1. Field of the Invention
The present invention relates to a semiconductor photo detector element such as a silicon photo diode (SPD) and a position sensitive device (PSD), distance measuring equipment for measuring a distance up to a target to be measured in distance using the semiconductor photo detector element, and a camera using the semiconductor photo detector element.
2. Description of the Related Art
There is widely spread a camera incorporating thereinto an automatic focusing (AF) device, which is generally referred to as an active type. Such an active type of automatic focusing device adopts a system for measuring a distance up to a camera subject in such a manner that an AF light projection unit and an AF photo detection unit are disposed at intervals of a predetermined base length, light is projected from the AF light projection unit to the camera subject, and light reflected on the camera subject is detected by the AF photo detection unit. As a photo detector element for focusing, for example, a semiconductor element, such as an SPD element and a PSD element, is used. By way of example, Japanese Patent Application Laid Open Gazette Sho. 57-22508 discloses a system in which a PSD element is used to perform focusing. In some cases, a camera is provided with an automatic flash emission device (an automatic electronic flash device), in which at the time of a photography, a flash is projected to a camera subject, a reflected light from the camera subject is detected, and a flash emission is stopped at a timing that the reflected light reaches a predetermined light quantity, and a remote control device for instructing an execution of an operation (for example, a self-time operation) according to a received light from a remote control equipment (for example, for a self-timer) for controlling the camera in accordance with an emission of light is directed to the camera, as well as an automatic focusing device. In such a case, in the camera, the automatic electronic flash device and the remote control device are provided with semiconductor photo detector elements represented by the SPD element, in addition to the semiconductor photo detector elements represented by the SPD element, in addition to the semiconductor photo detector element for the automatic focus (AF).
FIG. 9 is a diagram of semiconductor photo detector elements incorporated into the respective devices and their associated circuits, with respect to the conventional camera.
In FIG. 9, there is shown a PSD 61, which is one example of the semiconductor photo detector element for the automatic focus (AF), and an AF-dedicated photo detector circuit 62, which are provided in an automatic focusing device; and an SPD 63 provided in another device and a dedicated photo detector 64 for the another device. The AF-dedicated photo detector 62 and the dedicated photo detector circuit 64 are connected to an MPU (Micro Processor Unit) 65 serving as a control unit. Here, there will be explained a case wherein the camera is provided with an automatic electronic flash device as the "another device".
The PSD 61 shown in FIG. 9 generates a photo-current in such a manner that light for focusing is projected from an AF light projection unit (not illustrated) to a camera subject to the light for focusing reflected on the camera subject is detected on a detection surface of the PSD 61. The photo-current thus generated is separated into photo-currents I.sub.1 and I.sub.2 in accordance with distances between an irradiation position on the detection surface and both ends of the detection surface, respectively, and the photo-currents I.sub.1 and I.sub.2 are fed to the AF-dedicated photo detector circuit 62. The AF-dedicated photo detector circuit 62 determines a distance up to the camera subject in accordance with both photo-current I.sub.1 and I.sub.2. The MPU controls a driving lens for focusing in accordance with the distance thus determined.
On the other hand, the SPD 63 detects the reflected light from the camera subject through the flash projected to the camera subject from an automatic electronic flash device at the time of photography. A photo-current I.sub.3 generated through the detection by the SPD 63 conducts via the dedicated photo detector circuit 64. The dedicated photo detector circuit 64 integrates the photo-current I.sub.3 and outputs a signal to stop the flashing operation of the automatic electronic flash device in the timing that the integrated photo-current I.sub.3 reaches a predetermined quantity of reflected light. This signal is transmitted to the MPU 65 as well as a flash emission stop control unit (not illustrated). The MPU 65 performs a control of shutter closing and the like in accordance with this signal.
As mentioned above, in some case, the conventional camera is provided with an automatic electronic flash device and a remote control device as well as an automatic focusing device. In such a camera, although the photo detection wavelengths of those devices are mutually closed, those devices are individually provided with their dedicated photo detector elements. Thus, the conventional camera is associated with a problem that the number of photo detector elements is increased, and as a result a circuit scale is enlarged. Accordingly, there is also a problem that the cost is increased.
Further, there is proposed a technology (cf. Japanese Patent Application Laid Open Gazette Hei. 7-260475) in which instead of the AF-dedicated photo detector circuit 62, the signal of the photo-current is subjected to an A/D conversion and then is operated. However, also in accordance with this technology, the number of photo detector elements is large. This technology is also associated with a problem that the cost is increased.
In order to solve those problems, it is considered that one semiconductor photo detector element is used on a common basis for the automatic focusing device and another device. However, control and processing method for photo detection signals in the automatic focusing device are different from those in another device, for example, an automatic electronic flash device. Therefore, it is difficult for another device to use an AF-dedicated photo detector circuit for processing photo-current from the semiconductor photo detector element as a photo detector circuit as it is.
Further, the camera incorporated therein an automatic focusing device is also associated with an additional problem that as to focusing for distance, an accuracy of focusing is lowered.